Earth abundant organometal halide perovskites have emerged as a promising class of light emitting materials that may exhibit high color purity and tunability. While bulk perovskite thin films can be prepared by relatively facile low temperature solution processing, they often suffer from low photoluminescence quantum efficiency (PLQE), possibly due to emission quenching caused by defects. Although single crystalline nano/microscale perovskites have demonstrated high PLQEs, they have been prepared only by wet-chemistry methods. For example, green emitting nanoscale three-dimensional (3D) methylammonium lead bromide perovskites (MAPbBr3) prepared by wet-chemistry techniques have shown PLQEs up to 93%. (see, e.g., L. C. Schmidt et al. J. Am. Chem. Soc., 2014, 136, 850-853; S. Gonzalez-Carrero et al. J. Mater. Chem. A, 2015, 3, 9187-9193; H. Huang et al. Advanced Science, 2015, 2, 1500194; C. Muthu et al. Rsc. Adv., 2014, 4, 55908-55911; and O. Vybornyi et al. Nanoscale, 2016, DOI: 10.1039/c5nr06890h).
Highly luminescent two-dimensional (2D) layered lead bromide perovskite nano/microdisks with deep blue emissions also have been reported (S. Gonzalez-Carrero et al. J. Mater. Chem. A, 2015, 3, 14039-14045; P. Audebert et al. Chem. Mater., 2009, 21, 210-214; L. T. Dou et al. Science, 2015, 349, 1518-1521). In addition to higher PLQEs, these nanoscale perovskites also have shown purer and narrower emissions, and higher stability, as compared to their bulk counterparts. The methods used to synthesize these perovskites and others, however, typically are difficult, suffer from relatively low product yields, and/or do not produce high quality perovskites either consistently or at all.
Organometal halide perovskites also have been demonstrated to exhibit high color tunability across the visible to near infrared regions. This feature has been explored through synthetic control of 3D perovskite structures by using different halide anions, i.e., Cl, Br, I, and their mixtures (see, e.g., F. Zhang et al. Acs. Nano., 2015, 9, 4533-4542; D. M. Jang et al. Nano. Lett., 2015, 15, 5191-5199; N. Pellet et al. Chem. Mater., 2015, 27, 2181-2188; Y. H. Kim et al. Adv. Mater. 2015, 27, 1248-1254; and J. H. Noh et al. Nano. Lett. 2013, 13, 1764-1769).
The use of bulk quasi-2D layered lead(II) iodide perovskites with tunable absorptions as light absorber in photovoltaic cells (PVs) has been reported (I. C. Smith et al. Angew. Chem. Int. Edit., 2014, 53, 11232-11235; and D. H. Cao et al. J. Am. Chem. Soc., 2015, 137, 7843-7850). Although these hybrid perovskites have shown better moisture resistance than pure 3D perovskites, the color tuning of perovskites by organic cations remains challenging, due at least in part to the wet-chemistry techniques used to prepare them. This likely is due, at least in part, to the difficulty associated with controlling crystal growth in a solution phase containing different organic cations. Due at least in part to this difficulty, non-uniform products with impure emissions often are produced.
Also, the color tuning of lead (II) bromide perovskites by using organic cations to control the thickness of the obtained nanoplatelets has been reported, but the products suffer from relatively low quantum efficiency, and their emissions are not pure, i.e., include broad and multiple peaks, due at least to the fact that the process results in the formation of mixed perovskites having different thicknesses (J. A. Sichert et al. Nano. Lett., 2015, 15, 6521-6527).
Therefore, there remains a need for nanoscale metal halide perovskites that are stable, color tunable, exhibit narrow emissions, have high quantum efficiencies, and/or are capable of being made by a relatively simple process that may permit control over the crystalline structure of the nanoscale metal halide perovskites.